MADISON, Wis. (AP)  House Speaker Paul Ryan’s Republican primary challenger told a columnist for the New York Post in a Twitter message to “Eat a bullet.”

Paul Nehlen, who has built a reputation as a firebrand conservative backer of President Donald Trump, sent the tweet on Wednesday night. It came after a back and forth with Post columnist John Podhoretz that stemmed from a tweet Nehlen sent about a bill passed by the House that would make it easier for gun owners to legally carry concealed weapons across state lines.

Podhoretz tweeted to Nehlen: “Maybe you should eat something. Your brain needs nourishment. It’s the size of a pea.”

Nehlen tweeted in response: “Do us all a favor, Podhoretz. Eat a bullet.”

Nehlen posted a follow up message Thursday suggesting his comment was a joke. He tweeted an advertisement for a Dutch snack food called “Boston Bullet.”

Podhoretz did not immediately reply to a message seeking comment Thursday. Ryan’s campaign spokesman, Kevin Seifert, dismissed the tweets as “the latest embarrassing controversy that Paul Nehlen has created for himself.”